The wiping fabric of U.S. Pat. No. 3,668,658 comprises a porous, low-friction, anti-static material which may be a self-supporting dusting fabric.
U.S. Pat. No. 4,239,828 (Knope et al.) suggests that the wiping fabric may be a tissue-like material of synthetic fibers such as rayon and polypropylene fibers which have been fused together to afford integrity to the fabric. This is attached to a sheet of the jacket material by a single pass of a roll having knurled sections of about 3 mm in width which have been preheated to 175.degree. C. This fuses the fabric to the jacket sheet only at the knurl patterns without observable change in the overall porosity of the fabric. A lubricant pre-applied to the fabric is continuouly wiped onto the disk in use.
In most diskettes now on the market, the tissue-like wiping fabric is fused to a sheet of the jacket material in point-contact patterns as in U.S. Pat. No. 4,263,634 (Chenoweth et al.). Ultrasonic welding is sometimes employed instead of heat. Whether laminated by heat or by ultrasonic welding, there have been problems such as (1) delamination of self-supporting fabrics from the diskette jackets, (2) the fabric scratching the surface of the recording disk, especially by hard nodules created upon fusing the wiping fabric to the jacket sheet, and (3) the tendency of fibers to protrude from the wiping fabric into the jacket openings, thus creating the hazard that the protruding fibers might be picked up by the drive mechanism and become trapped at the gap of the recording heads. There has also been a problem of torque variations, especially when the fiber distribution in the fabric has been nonuniform.
It is believed that all commercial diskettes are fabricated by cutting the tissue-like wiping fabric to size and adhering the cut pieces one at a time to individual sheets of the jacket material, leaving edges of each jacket sheet uncovered. Each sheet is then die-cut to provide a jacket blank; two edges which are not covered by the wiping fabric are folded and heat-sealed or otherwise adhered to the outer surface of the jacket blank to provide an envelope; the recording disk is inserted; and a third uncovered edge is folded and then adhered to the outer surface to enclose the disk. There have been problems with adhesion of the folded edges to the underlying jacket material.
Most newly-designed diskette drives record data on both faces of the magnetic recording disk. In those drives, the recording head at Side 0 of the diskette is fixed and the opposing head at Side 1 is spring-loaded. Adjacent the heads is a jacket load pad which lightly presses the two layers of wiping fabric against the recording disk to wipe off any dust and debris. The fixed recording head is adjusted with respect to the fixed member of the jacket load pad so as to penetrate into the recording disk sufficiently to insure uniform signal response, even when the jacket wall (i.e., jacket material plus wiping fabric) at Side 0 has its maximum thickness. When the jacket wall has its minimum thickness, the recording head penetrates further into the recording disk, and while this still provides uniform signal response, it can produce undue wear both on the disk and on the head. Because of this, manufacturers of diskette drives would like to establish close tolerances for jacket wall thickness.
It is believed that of all diskettes now on the market, the thickness of the jacket material varies at least 2 mils (0.05 mm) and of the tissue-like wiping fabric varies at least 3 mils (0.075 mm). Hence, the best current thickness tolerance of the jacket walls is 5 mils (.+-.2.5 mils). Some have thickness variations up to 8 mils. A closer tolerance would permit the recording head to be adjusted to a lesser degree of penetration into the recording disk, thus reducing wear.